This project is our continued effort to elucidate the nonspecific aspects of local anesthetic actions. The study is directed at the thermodynamic and statistical mechanical analyses of the association of local anesthetics with lipids, phospholipid membranes, protein macromolecules and nerve cell membrane fragments. Special emphasis is placed at the interfacial action of the drugs. We have devised a method which measures separately the oil/water partition coefficients of charged and uncharged species. Application of this method demonstrated that the charged species of local anesthetics have nonzero oil solubility and that the uncharged species is not as lipophilic as generally believed. We found that local anesthetic molecules have a tendency to accumulate at the membrane/water interface regardless of charged or uncharged molecules. Amphipathy rather than lipophilicity appears to be the key factor for the nerve blocking action. We intend to include other local anesthetics during this project. The binding of local anesthetics to macromolecules and membrane fragments is measured by frontal gel chromatography and ultrafiltration techniques. The interfacial action will be measured by the surface tension method and analyzed according to our statistical mechanical theory. Under this theory, the forces of interfacial adsorption of local anesthetics are separated into 1) the arfinity potential of the drug molecule to the surface membrane, 2) the tendency to be excluded from water and 3) the cohesion among anesthetic molecules. This study was successfully performed with lidocaine and procaine and will be extended to include other anesthetics. Partition coefficients and binding constants are equilibrium quantities. They represent the change of the standard chemical potential of drug molecules caused by the transfer into organic domain. Therefore, these values are not a simple ratio of anesthetic concentrations; they provide information on the mechanism of how these molecules are incorporated into membranes and macromolecules in thermodynamic terms.